1. Field of the Invention
This invention relates to an electronic device and more particularly to a ground clip for connecting a ground plane of a printed circuit board to the electronic device chassis.
2. Background of the Relevant Art
A electronic device is one which carries forward electrical functions within the confines of an electronic device housing or chassis. The electronic device typically includes one or more printed circuit boards ("boards") rigidly held within the chassis. Each board is designed with printed conductors arranged upon one or more layers extending across the board. The printed conductors provide interconnect of components secured upon one or both outer planar surfaces of the board. As defined herein, "components" refer to integrated or discrete circuits well known in the semiconductor art.
Most industrial- and commercial-type boards are manufactured from rigid copper-clad, epoxy-impregnated glass fiber laminate. The printed conductors can be selectively formed by a subtractive or additive process. Either process includes tin, lead-tin, and/or gold plated upon the conductive material which forms the printed conductor. At the terminal ends of a set of printed conductors near the edge of the board is a row of edge-board contacts. The edge-board contacts are formed at the same time as the printed conductors, and are configured to allow mating of the board edge into a receptor connected upon the backplane surface of the electronic device chassis. Mating of the edge-board contacts to the receptor provides electrical communication of the components to the electronic device backplane.
Backplane connectivity is therefore carried out by laterally moving the board a spaced distance above, and relative to, the bottom portion (or base) of the electronic device chassis. It is important when effectuating the aforesaid connection that not only must the edge-board contacts securely mate with corresponding receptors, but it is equally important that any and all ground conductors within the board connect to the chassis. It would be desirable that ground conductor-to-chassis contact be made during board assembly to the backplane, and that the ground conductor be connected periodically along the chassis. Periodic electrical connection between the ground conductor and chassis is necessary to reduce voltage potential gradients within the ground conductor as well as within the chassis.
A ground conductor is formed during fabrication of a single layer or multi-layered board. The ground conductor is presented through photolithography as a printed conductive element extending across one or both outer planar surfaces of the board or within the board itself. In many instances, the ground conductor exists as a planar unit disposed within and entirely across a multi-layered board. When configured as a planar unit, the ground conductor serves to electrically decouple noise interference or cross-talk occurring between printed conductors insulatively spaced from the ground plane. It is preferable, therefore, that a multi-layered board have at least one ground conductor (or plane) configured within the board, and that the ground conductor be connected with maximum conductivity to a ground supply. To minimize voltage gradients and to maximize current-carrying capacity, it is further important that ground supply connection be made at spaced intervals along the ground conductor printed path.
The chassis of an electronic device is typically coupled to a ground supply via the third prong of a three-prong AC wall adapter. Among other reasons, a grounded chassis affords a grounded element which surrounds at least a portion of the board and components arranged across the board. The grounded chassis not only protects a user against shock when he or she touches the chassis but, more importantly, shields against deleterious amounts of electromagnetic interference (or "EMI") transmitted from the electronic device during operation. Reduction of EMI is not only necessary to meet consumer demand, but also provides a more reliable shield against noise interference and crosstalk often associated with EMI radiation. Connection of the ground supply to the chassis is relatively easy and is generally performed at the location in which the AC electrical cord enters the chassis. Reliable connection of the chassis to the ground conductor, however, is much more difficult.
There have been many conventional mechanisms used to electrically connect a chassis to a ground conductor. One popular mechanism involves placing a screw through the board and into the chassis. At the upper surface of the board is a conductive solder pad, onto which the lower surface of the screw head is designed to abut. The solder pad is coupled to the ground conductor through a via. The via is configured on the exposed planar surface of the board and/or is buried within the board itself. By tightening the screw into the chassis, the backside surface of the screw head contacts the solder pad resulting in an electrical path from the chassis to the ground conductor by way of the screw, solder pad and via. It is necessary that not only the hole through the board into which the screw is placed be aligned with the hole in the chassis, but it is also necessary that a via be reliably formed between the solder pad arranged on the upper surface of the board and all ground conductors formed upon and/or within the board. Placement of the screw is not only tedious and time consuming, but also must be performed with extreme care. Any slip of the tightening tool from the screw head to the board upper surface could not only damage the printed conductors or vias arranged thereon, but could also, in extreme cases, pierce or crack the insulative glass fiber laminate. Still further, tightening of the screw head backside surface upon the solder pad can dislodge solder particles from the solder pad which can migrate from the solder pad and possibly lodge between printed conductors, edge-board contacts and/or receptor contacts. Vibration or any type of relative motion between the screw head and underlying board caused, for example, by an operable electronic device or periodic movement of that device can, over time, result in reliability problems. Movement of the electronic device may cause the screw to loosen in a counter fashion or, more likely, movement of the device may cause dislodgement of solder underneath the head as the head moves relative to the solder pad. Movement of the head causes the head to sweep the relatively soft solder from the pad, resulting in eventual separation between the head and the solder pad. Any separation between the grounded screw and the solder pad will force an open circuit therebetween. An improperly grounded ground conductor can effect the operability of each and every component coupled to the ground conductor. It is therefore important that an alternative chassis-to-ground conductor connection be made which is less labor intensive, is less prone to user error, is less susceptible to solder dislodgement during assembly and operation, and is generally more reliable.
It would be desirable to employ a chassis-to-ground conductor attachment mechanism which avoids the use of a screw or any user-assembled, tightening-type fastener. The attachment mechanism must be one which is pre-assembled as part of the board. Moreover, to minimize the complexity of the attachment process, the desired attachment mechanism should allow mating of the ground conductor, at periodic intervals across the ground conductor, to the chassis at the same time in which the edge-board contacts are mated with the backplane receptor. The backplane receptor is defined as a receptor configured at the rear surface of the sheet metal chasis. The attachment mechanism must further be designed to allow removal of the board from the chassis without having to "re-work" the chassis-to-ground conductor contact points. More specifically, heating the contact points to relieve attachment of the board from the chassis must be avoided. Re-work heating of the contact points may jeopardize the solder connections of the components upon the board.